Three types of instrument are presently available intended to grasp the head of a fetus in order to extract it from the natural genital tract of the mother, with the aim of shortening the period of delivery in cases of fetal distress or an arrest in the descent of the fetus head. These instruments are the forceps, the vacuum extractor and the spatulas.
As is known, the forceps is a pincer with two arms which is said to date from Roman times, but whose modern forms date from the 16th century. There are forceps with crossed arms and forceps with parallel arms. The forceps which have crossed arms, articulated on each other, and in which the "jaws" or "spoons" of the pincer present a cephalic curvature adapting to the fetus head and a pelvic curvature adapting to the pelvic floor of the mother, comprise means for pulling on the spoons, the best adapted of these means being those included in the TARNIER forceps.
The forceps with parallel arms developed by DEMELIN eliminates the problems of articulation caused by the forceps with crossed arms. In this second type of forceps, the uncrossed arms, articulated by means of a screw, at the level of the handles extending the spoons, which can be tightened as desired, thus protecting the fetus head, have been replaced by forceps with parallel arms which are made integral by means of a transverse arm and on which cords can be attached.
It should be noted that in 1860 CHASSAGNY had suggested attaching cords to arms carried by the spoons in forceps with crossed arms, and intended to permit the application of traction forces on the spoons in the proximity of the fetus head; however, these cords were unable to observe the pelvic curvature, so that this forceps was quickly abandoned to the benefit of the TARNIER forceps.
It was in 1950 that the THIERRY spatulas were proposed, which consist of two completely independent spoons and which do not therefore constitute a pincer. These two symmetrical spatulas comprise a solid spoon with a facial curvature and pelvic curvature, and a rectilinear handle having at its free end notches for receiving the fingers of the obstetrician; their purpose is to simulate, in the fetus head, movements similar to the physiological movements, but while at the same time respecting its mobility.
The obstetric vacuum extractors for extracting a fetus are made up of three main elements: a gripping system, a pulling device and a vacuum generator.
The gripping system is made up of a cup, or metallic extractor, of a diameter suitable for providing a sufficient adherence. The pulling device is made up of a metal plate held at a slight distance from the extractor and in whose center there is attached a small metal chain which passes through the inside of a flexible rubber tube itself connected to the outer orifice of the extractor and at the opposite end of which there is fitted a cruciform metal handle, one of the hollow branches of which permits the introduction of a rod engaging the pulling chain. The vacuum generator is made up of a vacuum pump provided with a manometer and functioning by hand.
In order to prevent the possible traumatic effects of the metal instruments, flexible systems such as tapes, slings or nets have been proposed for fetus extraction, particularly in Japan in the 18th century; among these, a pliable whalebone collar intended to be passed round the end of the fetus and connected at its opposite end to a wooden handle used for pulling; a piece of silk connected to a silk tape for pulling.
The obstetric extractor by Dr. John EVANS (CHICAGO, middle of 19th century) is also known, this being made up of two parallel steel arms with a curve for following the bottom of the sacrum and a joint permitting relative mobility near the end of the curved segment, while the parallel bars were held together by means of a flat clasp, on the handles, during the introduction of the curved ends into the pelvis; a net of silk tape intended to surround the fetus head was fixed to the curved end arms. Following introduction, the clasp was removed, the arms were separated and one of them was passed by way of the opposite side of the pelvis, in such a way as to encircle the fetus head in the net. With the aid of the long tapes of the net, which hung from the vagina, the obstetrician exerted a pull alternately on each of their attached ends and on the steel arms in order to bring about the descent of the fetus head. The efficiency of this type of extractor with parallel arms, without any transverse arm or articulation screw has not been demonstrated, and so it has not gained recognition in practice.
There has also been proposed, in German Patent Application HEEGE No. 2,233,840, an obstetric apparatus which comprises a crosslinked tube whose front part is provided with a dilatable edge, this tube being arranged in a gripping sleeve and being capable of being widened at least as far as the size of a neonate's head using flexible guide rods which are mounted displaceably in said sleeve and are attached to the abovementioned edge.